Conventionally, microfabrication by lithography using photoresist compositions has been performed in the production of semiconductor devices. This microfabrication is a fabrication method that includes forming a thin film of a photoresist composition on a substrate to be fabricated such as a silicon wafer, irradiating active rays such as ultraviolet rays onto the thin film through a mask pattern in which a pattern of a semiconductor device is formed, developing the film, and etching the substrate to be fabricated such as a silicon wafer using the obtained photoresist pattern as a protective film. In recent years, higher integration of semiconductor devices has been pursued, and there is a trend for the active rays used to have shorter wavelengths from KrF excimer lasers (248 nm) to ArF excimer lasers (193 nm). This trend has been accompanied by significant issues of influences due to standing waves and diffuse reflection of the active rays by irradiation from the substrate. Accordingly, methods have been extensively studied that include providing an anti-reflective coating (Bottom Anti-Reflective Coating, BARC) between the photoresist and the substrate to be fabricated.
As a finer resist pattern is further pursued, an issue of resolution and an issue in which the resist pattern formed collapses after development may occur, and thus thinner resists are required to solve these issues. However, in producing such thinner resists, it is difficult to achieve sufficient resist pattern film thickness for fabrication of a substrate, and thus a process has become necessary in which the function of a mask during the substrate fabrication is imparted not only to the resist pattern, but also to a resist underlayer film that is formed between the resist and a semiconductor substrate to be fabricated. As a method for achieving such a thinner film thickness of resists, a lithography process is known in which at least two layers of resist underlayer films are formed, and the resist underlayer films are used as etching masks. The resist underlayer films for the lithography process need to have high etching resistance to an etching gas (e.g., fluorocarbon) in a dry etching process.
As the resist pattern becomes finer, irregular bending of the pattern called “wiggling” may occur in the resist underlayer films as etching masks during a dry-etching process, thereby hindering desired pattern formation during the semiconductor substrate fabrication. Thus, the resist underlayer films as etching masks require underlayer film material having high wiggling resistance that can suppress occurrence of the wiggling even in fine patterns. The resist underlayer films also require a resist underlayer film-forming composition having planarizing properties and embeddability that enable level differences or irregular portions formed on surfaces of semiconductor substrates to be sufficiently coated.
The following are examples of a polymer for the resist underlayer film described above.                Resist underlayer film-forming compositions each including polyvinyl carbazole are exemplified (see Patent Document 1, Patent Document 2, and Patent Document 3).        A resist underlayer film-forming composition including a fluorene phenol novolac resin is described (see Patent Document 4, for example).        A resist underlayer film-forming composition including a fluorene naphthol novolac resin is described (see Patent Document 5, for example).        Resist underlayer film-forming compositions each containing fluorene phenol and aryl alkylene as repeating units are described (see Patent Document 6 and Patent Document 7, for example).            A resist underlayer film-forming composition including carbazole novolac is described (see Patent Document 8, for example).    A resist underlayer film-forming composition including a polynuclear phenol novolac is described (see Patent Document 9, for example).